Nondestructive and in-situ monitoring of mechanical property buildup in epoxy adhesives for civil applications by propagation of ultrasonic waves

Ultrasonic inspection for nondestructive analysis is already widely applied to the control of structural integrity of concrete, presenting among other advantages the reliability, the simplicity and low costs. Although ultraso nic testing are mainly used for nondestructive evaluation of defects, it ma y be also applied to follow the changes of mechanical properties occurring in a material which evolves in time, such as during the crosslinking of the rmosetting resins. These time dependent properties may be measured by longi tudinal and shear ultrasonic velocity operating by pulse-echo and/or throug h-transmission methods. In this work, ultrasonic wave propagation has been applied to the monitoring of the progress of the curing reaction of an epox y adhesive for civil applications. The data have been collected in isotherm al conditions on the neat resin, as well as in a coupled system concrete-re sin-concrete. The measurements of longitudinal and shear velocity have been used for the calculation of Young and shear moduli. The change of velocity during cure must be considered a powerful tool for the measurement of the progress of ambient temperature cure reactions like in the case of adhesive s for civil applications.